How to simulate uneven paint fading?
Start with the animation showing the light patterns.



By baking the shadow from this animation to the surface, the light at each time step is determined.



Using GIMP, the average amount of light on the surface can be calculated from the frames in the baked shadow animation. The lighter areas will fade more than the darker areas.



Then, by combining the average shadow map with the original texture and using nodes, the faded texture is created. The node network to combine the shadow map with the texture is:



Where the average light was low, the original texture is preserved. However, where the average lighting was high, the texture is faded.





The original and faded texture follow.